Two-dimensional electron gases in Ga-face and N-face AlGaN/GaN heterostructures grown by plasma-induced molecular beam epitaxy and metalorganic chemical vapor deposition on sapphire

• Published in: Journal of applied physics Vol. 87; no. 7; pp. 3375 - 3380
• Main Authors: Dimitrov, R., Murphy, M., Smart, J., Schaff, W., Shealy, J. R., Eastman, L. F., Ambacher, O., Stutzmann, M.
• Format: Journal Article
• Language: English
• Published: 01.04.2000
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.372353

We report on the growth of nominally undoped GaN/AlxGa1−xN/GaN (x<0.4) high mobility heterostructures with N-face or Ga-face polarity on sapphire substrates by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic chemical vapor deposition in order to study the formation and electrical transport properties of polarization induced two-dimensional electron gases (2DEGs). By depositing a thin AlN nucleation layer on the sapphire substrates before the growth of a GaN buffer layer by PIMBE, we were able to change the polarity of the wurtzite films from N to Ga face. The switch in the polarity causes a change in the sign of the spontaneous and piezoelectric polarization directed along the c axis of the strained AlGaN barrier. As a consequence the polarization induced 2DEG is confined at different interfaces in heterostructures with different polarities. The transport properties of the 2DEGs in Ga- and N-face heterostructures were investigated by a combination of capacitance–voltage profiling, Hall effect, and Shubnikov-de Haas measurements. Dominant electron scattering mechanisms are studied in order to provide the knowledge necessary for further improvements of the electron transport properties and performance of AlGaN/GaN based “normal” (based on Ga-face heterostructures) and “inverted” (based on N-face heterostructures) high electron mobility transistors.